This study will continue to explore the interrelationships between malignancy and immunity in the Gross passage A virus-mouse system. Attempts will be made to determine what specific factors are involved in the leukemogenic process. This study will incorporate a variety of experimental approaches: 1) The virus-host interactions will be explored by analyzing the virus, its sources, routes of introduction to the host, its sites of action, and dissemination throughout the host; 2) The immune response mechanism to virus during leukemogenesis will be studied; and 3) Attempts will also be made to heighten the immune response to bring about a remission or a rejection of the malignancy. BIBLIOGRAPHIC REFERENCES: Mariani, T.: Immunologic competence of Gross passage A preleukemic C3H/Bi inbred mice. Fed. Proc. 35:387, 1976. Landucci, G. and Mariani, T.: Horizontal transmission of Gross leukemia by organ transplants. Fed. Proc. 35:737, 1976.